Appendages

An appendage is a projecting part of an organism's body that extends from the main body and serves a function such as movement, sensing, feeding, or reproduction. In animals, common appendages include limbs, tails, fins, antennae, and jaws or mouthparts.

In arthropods, appendages are typically segmented and jointed, and can be adapted for walking, grasping, feeding, or sensing; examples include legs, antennae, mandibles, wings, and cerci. In vertebrates, paired limbs (arms and legs) arise from limb buds during embryonic development, while tails and fins provide balance or propulsion. Many marine vertebrates have fins that act as paddles or rudders.

Development and evolution: Appendages arise from embryonic outgrowths called buds or folds; their development is governed by gene networks including Hox genes and signaling pathways that pattern identity along the axis. Across evolution, appendages are often modified for specific uses, a process including fusion, reduction, or loss of function, and can be repurposed for new roles (exaptation).

Function and variation: Appendages enable locomotion, manipulation of objects, sensory perception, feeding, defense, and mating. Some species display highly specialized appendages, such as octopus arms with suckers, butterfly antennae for smell, or insect mouthparts adapted to different diets. In some lineages, appendages are reduced or absent as lifestyles change.